1. Field of the Invention
The present invention relates to gas turbine engines, and more particularly, to turbine blade shroud seals for reducing the leakage of cooling fluid in the casing surrounding the turbine blades.
2. Description of the Prior Art
There have been many attempts to improve the sealing capabilities of annular shrouds surrounding the tips of turbine blades. The engine casing surrounds the turbine section of an aircraft engine and is constructed to conduct cooling gases within the casing to various elements, such as the shrouds themselves. The turbine section of the engine, which is concentric to the casing, is in the path of very hot gases. It is preferred that the surrounding casing structure be maintained relatively cool.
The annular shroud for the turbine blade tips is normally segmented in the circumferential direction. Seals are required to prevent gas leakage at the gaps formed between the ends of the shroud segments. U.S. Pat. No. 4,767,260 to Clevenger et al, issued Aug. 30, 1988, and U.S. Pat. No. 5,158,430 to Dixon et al, issued Oct. 27, 1992, show variations on feather seals placed between the platforms of the vane assemblies. U.S. Pat. No. 4,573,866 to Sandy, Jr. et al, issued Mar. 4, 1986, shows a feather seal in a radial plane between the ends of the blade tip shrouds. U.S. Pat. No. 5,318,402 to Bailey et al, issued Jun. 7, 1994, shows a spline or feather seal and a circumferential spacer band that locks the shrouds and the feather seals together.
Different sealing rings are also required for different shroud and casing configurations. For instance, in a configuration involving a split joint with a groove having an axial component, it is conventional to use a "C" shaped ring. In U.S. Pat. No. 4,573,866, a bellows type ring is utilized in such a groove. Although such ring seals provide excellent sealing qualities, they tend to be stiff in compression due to the radial cross-section thereof and are, therefore, not easily replaced during engine maintenance. In fact, special tools may be required to replace such a seal.